For preventing surging of a gas turbine, there have been the following types of apparatus:
A. The apparatus which controls the fuel supply by detecting the turbine inlet gas temperature or the temperature directly associated with the turbine inlet gas temperature and feeding it back to the fuel control valve. This apparatus, however, has a number of defects as follows:
A. As the turbine inlet gas temperature which ranges from 900.degree. C. to 1,200.degree. C. usually differs from one place to another by 50.degree. C. to 100.degree. C., it is very difficult to get the average gas temperature at the turbine inlet.
B. High temperature of such gas decreases the durability and accuracy of the temperature detector.
C. Owing to its heat capacity, the temperature detector can not instantaneously follow the change in temperature of the gas; therefore the real temperature of the gas can only be detected with a certain time lag. Additional means is required to compensate for this time lag, but none of such means known in the art is very reliable, despite its complicated structure.
D. In order to make up the low accuracy and low responsiveness of the temperature detector, it is necessary to establish an excessively safe or conservative control pattern, from which no highly efficient control of fuel supply can be expected.
E. The basic problem with this type of apparatus resides in its attempt to prevent surging which is due to an abrupt change in air pressure, by controlling fuel supply in response to change in the turbine inlet gas temperature.
B. The apparatus according to the so-called CDP-bellows method in which a signal corresponding to the pressure PCD of air at the compressor outlet is transmitted to the bellows, thereby operating the needle valve associated therewith for controlling fuel supply. This apparatus also has a number of defects.
a. This mechanism is intended primarily for an aircraft gas turbine operating with a high pressure ratio which changes within the range wherein surging is apt to occur. A gas turbine for a motor car is provided with a heat exchanger to reduce fuel consumption and is necessarily adapted to operate at a low pressure ratio wherein the compressor outlet air pressure PCD hardly changes within the range wherein surging is apt to occur. Thus, the CDP-bellows method is not applicable to gas turbines for motor cars, but can only be used for a complicated hydro-mechanical fuel supply control system.
b. The hydro-mechanical system does not permit a highly efficient fuel supply control.
c. This apparatus does not allow any rectification against clogging of air filters or environmental changes, for example, of ambient pressure or temperature, to which motor cars are frequently subjected. The information necessary for preventing surging of the gas turbine is the pressure ratio in the compressor, i.e., PCD/pressure at the air intake, but the bellows receives in principle (PCD - (Pressure at the air intake)). This apparatus also does not allow any rectification for the change in ambient temperature.